title: CPT-11 sensitivity in relation to the expression of P170-glycoprotein and multidrug resistance-associated protein.
abstract: The relevance of P170-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) for the sensitivity to CPT-11 was investigated in human malignant cell lines as well as in human tumour xenografts. In vitro, the P-gp-positive sublines BRO/mdr1.1 (transfected with MDR1) and 2780AD were slightly cross-resistant against carboxylesterase-activated CPT-11. Cross-resistance against SN-38 was present in 2780AD cells, but not in BRO/mdr1.1 cells. The P-gp modulators BIBW22BS, verapamil and dexniguldipine partly reversed the resistance against CPT-11 in the P-gp-positive sublines. BIBW22BS was the most effective modulator in the reversal of the resistance against carboxylesterase-activated CPT-11 as well as against SN-38 in the 2780AD subline. In contrast to doxorubicin and vincristine, the BRO/mdr1.1 xenografts were at least as sensitive to CPT-11 as the BRO xenografts. The 2780AD xenografts were slightly less sensitive than the parent tumours, but there was no difference in topoisomerase I DNA unwinding activity. Therefore, the high retention of the multidrug-resistant phenotype of 2780AD cells in vivo may be the cause of the low cross-resistance against CPT-11. The MRP-positive subline GLC4/ADR was cross-resistant against carboxylesterase-activated CPT-11 and SN-38. GLC4/ADR cells, however, demonstrated a twofold lower topoisomerase I activity than GLC4 cells. Cross-resistance against the camptothecin derivatives was not apparent in the MRP-transfected subline of SW1573/S1. In conclusion, P-gp-positive cells show a low cross-resistance against CPT-11/SN38, which is only apparent with high P-gp expression in vivo. MRP does not seem to play a role in the sensitivity to CPT-11.
authors.affiliation: Department of Medical Oncology, Academic Hospital Vrije Universiteit, Amsterdam, The Netherlands.
authors.forename: W J
authors.initials: WJ
authors.lastname: Jansen
authors.forename: T M
authors.initials: TM
authors.lastname: Hulscher
authors.forename: J
authors.initials: J
authors.lastname: van Ark-Otte
authors.forename: G
authors.initials: G
authors.lastname: Giaccone
authors.forename: H M
authors.initials: HM
authors.lastname: Pinedo
authors.forename: E
authors.initials: E
authors.lastname: Boven
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000502:physiology*; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology; D004264:DNA Topoisomerases, Type I / Q000235:genetics; D005260:Female; D006801:Humans; D000077146:Irinotecan; D051379:Mice; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger / Q000032:analysis; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D000972:Antineoplastic Agents, Phytogenic; D002166:Camptothecin; D004264:DNA Topoisomerases, Type I; D000077146:Irinotecan; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger; D014700:Verapamil